1. Field of the Invention
The present invention relates to a vehicle passenger detecting device, which determines whether or not a passenger seated on a seat of a vehicle is a child seated through a child restraint system such as a child seat, for example.
2. Description of Related Art
There has been, conventionally, known a passenger detecting device in which load sensors 3 are incorporated to four supporting leg portions 2 for supporting a seat 1 of a vehicle, respectively, so as to judge whether a passenger is an adult or a child by an output value of each of the sensors, as shown in FIG. 6 (for example, reference to page 3-4, FIG. 3 in JP-A-2003-246256).
When a seat portion 1a of the seat 1 is zoned into four areas from front to back and from side to side (front inner area, front outer area, rear inner area and rear outer area), each of the supporting leg portions 2 in which the load sensor 3 is incorporated is disposed corresponding to each of the areas, so as to support each of the areas. These supporting leg portions 2 are movable along a pair of seat rails 4, so the seat 1 is movable in a back and forth direction of the vehicle along the seat rails 4. In addition, the seat 1 is supported to be lockable in a predetermined back and forth position.
The weight of the passenger seated on the seat 1 is calculated from the total value of the detected value output from each of the load sensors 3. It is judged whether the passenger on the seat 1 is an adult or a child by the comparison of this calculated value with a threshold for judging an adult and a child.
In addition, if a child restraint system as a child seat (not shown) (hereinafter referred to as CRS) is installed on the seat 1 by a seat belt device 5, the CRS having stiffness tends to incline in the right and left direction by the pull force of the seat belt 5a of the seat belt device 5, so if the CRS is installed, a load difference is produced in the right and left of the seat portion 1a of the seat 1. Accordingly, the usage of the CRS can be detected.
On the contrary, if the passenger seated on the seat 1 is an adult, the tension of the seat belt 5a is absorbed by the body of the passenger, so if the seat belt device 5 is fastened, more particularly, the seat belt 5a is fastened, such a load difference is not produced as far as the passenger is seated on the central portion without being seated on one side of the seat portion 1a. 
Therefore, it can be determined whether the passenger is a child or not by a load difference acting on the seat portion 1a of the seat 1 with the seat belt 5a is fastened.
If it is judged that the passenger is an adult, a passenger protection device such as an air-bag device is operated when possibly having an impact on the passenger. In addition, if it is judged that the passenger is a child, the operation of such a passenger protection device is controlled or blocked, so as to prevent the child from being damaged by the passenger protection device.
However, with the detecting device set forth in JP-A 2003-246256, if a lightweight adult is seated on one side of the seat 1a of the seat 1, a load difference to be produced in the right and left, i.e., the both sides, of the seat portion 1a approaches a load difference to be produced in a seat belt fastened state for installing the CRS. In this case, an adult and a child using the CRS may be misjudged.